Any reason why I couldn't use the factory D30 vent hole as the bulkhead fitting for the ARB? I would retap it to 1/4 pipe and use the fitting below to connect everything. The air line is only 3MM and the ID of the fitting is 9mm. Should be enough to vent. I don't have the room on top of the diff to drill the hole unless I clear a spot of the truss I plan to add.

The red line in the pic would be the tube from the locker to the bulkhead fitting.